In 2016, PTFI produced approximately 59 million metric tons of tailings, which were managed using a controlled riverine tailings management system approved by the Government of Indonesia. This system includes the use of a fast-moving, unnavigable river system originating near the mill/processing area in a steep valley at an approximate 3,000 meter elevation to transport the tailings to an engineered and managed tailings deposition area in the lowlands portion of the PTFI Project Area. Levees have been and continue to be constructed to laterally contain the footprint of the tailings and to limit their impact in the lowlands. The system was chosen and approved following numerous technical studies (including 14 tailings transport and disposal options) and a multi-year review process including an Environmental Impact Study and an Ecological Risk Assessment. More conventional management systems were rejected due to the extreme terrain in a seismically active area with high precipitation, which created unacceptably high risks of catastrophic failure. Periodic independent environmental audits confirm that the company's tailings management plan represents the best alternative, considering the applicable geotechnical, topographic, climatological and seismic conditions. The management of tailings in the lowlands is the largest contributor to the footprint of disturbed areas. The Modified Ajkwa Deposition Area (ModADA) is the term used to describe the terrestrial portion of the designated tailings management area, covering approximately 230 square kilometers with east and west levees preventing lateral distribution of tailings and natural sediment.
Whereas our North American and South American TSFs utilize the TST and TRB for review and inspection, PTFI uses the ModADA Management Board (MMB) for oversight. The MMB is a multi-disciplinary expert panel that meets on-site approximately twice each year to assess performance and risks associated with the ModADA and coastal zone area. The MMB focuses on the structural integrity of the levees and the geochemical stability of the deposition area, as well as associated stakeholder engagement. The MMB provides recommendations to PTFI leadership and engineering teams on priority activities and tracks progress on all associated detailed recommendations. The MMB follows up on actions related to all recommendations during its onsite reviews.
PTFI has a tailings and river management department with dedicated management, engineers, lab services and operations for tailings activities. Members of PTFI’s external design team and internal management and engineering experts have been involved with its tailings management system for decades, providing continuity of services and support for the operating team while continuing to add resources to stay abreast of good practices. For example, the design team recently completed an updated site-specific hydrology study for the approximate 750 square kilometer watershed of the PTFI operations and adjacent river systems using updated data collected and scientific analyses for rainfall and runoff procedures.
At PTFI, overburden stockpiles are subject to erosion caused by the large amounts of rainfall in the region (average annual rainfall is 200 inches). The eroded stockpile material is eventually deposited in the tailings management area in the lowlands. This additional material, while predicted in our environmental studies, influences both the amounts and timing of deposition of finer tailings material in the estuary.
Impacts associated with controlled riverine tailings management include the smothering of vegetative cover inside the boundary of the ModADA, as well as sedimentation impacts to benthic (bottom-dwelling) organisms. The fraction of tailings and non-tailings sediment that are not retained within the deposition area, along with natural sediment from the adjacent Minajerwi watershed, are building new islands and wetland areas in the Ajkwa estuary below the ModADA. Several independent lines of evidence show that these impacts on the benthic community are physical in nature, temporary and reversible at the end of mine life.
The monitoring of terrestrial areas that are now outside the active tailings management area, but which received tailings for several years, shows rapid establishment and colonization by native plants. These areas of natural succession are abundant and are routinely monitored to determine plant community composition and recolonization rates. Areas now more than 10 years removed from deposition are in secondary growth. Data from biological sampling continue to also demonstrate that the estuaries downstream of the tailings deposition area are functioning ecosystems, based on both the number of species and the number of specimens collected of nektonic, or free-swimming, organisms such as fish and shrimp. Large-scale demonstration projects show that several land use options are possible after final closure of the deposition area. When mining is completed, the deposition area will be reclaimed with natural vegetation or used for agriculture, forestry, grazing of livestock or aquaculture. PTFI believes the area will fully recover after mining ceases based on several lines of evidence, including the recovery of natural succession in areas that were formerly impacted by tailings.
For more information on this topic, including our extensive biological monitoring system and beneficial use of tailings opportunities, please see the Controlled Riverine Tailings Management at PTFI summary document.
PHOTO DESCRIPTION: Since PTFI began quarterly monitoring programs of birds inhabiting Ajkwa Island in 2009 and Waii Island in 2012, the number of species observed annually has increased from 46 to 122, including a tripling of migratory bird species.